Seeing Central African forests through their largest trees J. Bastin, N. Barbier, M. Réjou-Méchain, A. Fayolle, S. Gourlet-Fleury, D. Maniatis, T. de Haulleville, F. Baya, H. Beeckman, D. Beina, et al. To cite this version: J. Bastin, N. Barbier, M. Réjou-Méchain, A. Fayolle, S. Gourlet-Fleury, et al.. Seeing Central African forests through their largest trees. Scientific Reports, Nature Publishing Group, 2015, 5 (1), 10.1038/srep13156. hal-01892195 HAL Id: hal-01892195 https://hal.umontpellier.fr/hal-01892195 Submitted on 3 Jun 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License www.nature.com/scientificreports OPEN Seeing Central African forests through their largest trees J.-F. Bastin1,2,3, N. Barbier4, M. Réjou-Méchain4,5, A. Fayolle2, S. Gourlet-Fleury5, D. Maniatis6, T. de Haulleville2,7, F. Baya8, H. Beeckman7, D. Beina9, P. Couteron4, Received: 03 December 2014 G. Chuyong10, G. Dauby11, J.-L. Doucet2, V. Droissart4, M. Dufrêne2, C. Ewango12, Accepted: 17 July 2015 J.F. Gillet2, C.H. Gonmadje5,13,14, T. Hart15, T. Kavali16, D. Kenfack17, M. Libalah4,21, Y. Malhi6, Published: 17 August 2015 J.-R. Makana12, R. Pélissier4, P. Ploton4, A. Serckx3,18,19,20, B. Sonké21, T. Stevart22, D.W. Thomas23, C. De Cannière1 & J. Bogaert2 Large tropical trees and a few dominant species were recently identified as the main structuring elements of tropical forests. However, such result did not translate yet into quantitative approaches which are essential to understand, predict and monitor forest functions and composition over large, often poorly accessible territories. Here we show that the above-ground biomass (AGB) of the whole forest can be predicted from a few large trees and that the relationship is proved strikingly stable in 175 1-ha plots investigated across 8 sites spanning Central Africa. We designed a generic model predicting AGB with an error of 14% when based on only 5% of the stems, which points to universality in forest structural properties. For the first time in Africa, we identified some dominant species that disproportionally contribute to forest AGB with 1.5% of recorded species accounting for over 50% of the stock of AGB. Consequently, focusing on large trees and dominant species provides precise information on the whole forest stand. This offers new perspectives for understanding the functioning of tropical forests and opens new doors for the development of innovative monitoring strategies. 1Landscape Ecology and Plant Production Systems Unit, Université libre de Bruxelles, CP264-2, B-1050 Bruxelles, Belgium. 2BIOSE Department, Gembloux Agro-Bio Tech, Université de Liège, B-5030 Gembloux, Belgium. 3Ecole Régionale post-universitaire d’Aménagement et de gestion Intégrés des Forêts et Territoires tropicaux, Kinshasa, DR Congo. 4UMR AMAP, IRD, F-34000 Montpellier, France. 5UPR BSEF, CIRAD, Campus International de Baillarguet, F-34398 Montpellier, France. 6Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK. 7Laboratory for Wood Biology and Xylarium, Royal Museum for Central Africa, Tervuren, Belgium. 8Ministère des Eaux, Forêts, Chasse et Pêche, BP 3314 Bangui, Central African Republic. 9Université de Bangui – Cerphameta, BP 1450 Bangui, Central African Republic. 10Department of Plant and Animal Sciences, University of Buea, P.O. Box 63, Buea, Cameroon. 11Laboratoire d’Evolution Biologique et Ecologie, Faculté des Sciences, Université libre de Bruxelles, CP160-12, Brussels, Belgium. 12Centre de Formation et de Recherche en Conservation Forestière (CEFRECOF), Wildlife Conservation Society, Kinshasa, DR Congo. 13National Herbarium, P.O BOX 1601, Yaoundé, Cameroon. 14CIFOR, Central African Regional Office, P.O. Box 2008 Messa, Yaoundé, Cameroon. 15Lukuru Wildlife Research Foundation, Kinshasa, Gombe, DR Congo. 16Wildlife Conservation Society - DRC Program, Kinshasa, DR Congo. 17CTFS-ForestGEO, Department of Botany, MRC 166, Smithsonian Institution, P.O. Box 37012, Washington, DC 20013-7012, USA. 18Behavioural Biology Unit, University of Liege, Liege, Belgium. 19Conservation Biology Unit, Royal Belgian Institute of Natural Sciences, Brussels, Belgium. 20Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany. 21Plant Systematic and Ecology Laboratory, Department of Biology, University of Yaounde 1, Yaounde, Cameroon. 22Missouri Botanical Garden, Africa and Madagascar Department, St Louis, MO, USA. 23Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA. Correspondence and requests for materials should be addressed to J.-F.B. (email: [email protected]) SCIENTIFIC REPORTS | 5:13156 | DOI: 10.1038/srep13156 1 www.nature.com/scientificreports/ Figure 1. Site locations. Spatial distribution of the study sites superimposed in white on a false color of Enhanced Vegetation Index (EVI) composite map centred on Central Africa. The map was produced from a yearly synthesis from twelve MODIS-EVI 250 m data (MOD13Q1 c5). The 8th, 1st and 8th, 16-day periods are projected in red, green and blue color channels. Copyright Dr. Valery Gond. Large trees play an important role in forest structure, functioning and diversity1. They provide nesting sites and shelter for up to 30% of all vertebrate species2, produce food1 and support a wide diversity of epiphytes and lianas. Towering above the canopy, large trees both enhance and regulate forest regen- eration and species coexistence by attracting dispersers, pollinators, herbivores and pathogens3,4. They influence understory species composition by preempting light and impacting local microclimates5 and their dead material can persist for decades which provides key habitat for ground fauna. And recently because large trees play a major role in the global carbon cycle1, they have become a focus of forest carbon research6–9. In tropical forests, large trees concentrate a large fraction of forest carbon stocks within their above-ground biomass (AGB)10, and they accumulate carbon faster than smaller trees8. Therefore, the AGB of the largest tropical trees may be a good indicator of AGB dynamics as a whole. For instance, the density of trees with a diameter at breast height (DBH) greater than or equal to 70 cm explained almost 70% of the variation in AGB among 120 pantropical sites6. However, large trees represent a small fraction of all tree individuals, so that they are easily over or under-represented by small sampling plots, poten- tially leading to high sampling errors in AGB estimation11. The metabolic scaling theory12,13 predicts that the inverse relationship between tree size and abundance does not vary within natural forests, i.e. here considered as a forest whose dynamics is only driven by ecological processes. Therefore, the structure of the entire forest can be approximated from the abundance of trees in a given size class. Both theoretical and empirical approaches13–15 have shown that non-competition induced mortality (e.g., mortality due to drought, fire or wind blowdown events1,16) could lead to a systematic overestimation of the density of large trees when using the metabolic scaling theory. Yet, because these deviations do appear to be sys- tematic13, the density of large trees should still convey information about the structure of the understory tree community. Recent studies conducted on the entire Amazonian basin showed that a small number of species con- tribute disproportionately to the global stem density and biomass, as they estimated that only 1.4% of tree species account for the half of the regional stem abundance17 and only 0.91% of tree species account for the half of the regional AGB18. These species were considered respectively as ‘stem hyperdominant’ and ‘biomass hyperdominant’. Identifying these key species is important to better understand the structure and the functioning of tropical forests19, and to develop effective monitoring and conservation strategies. This is of particular importance in Central Africa, the second largest area of continuous rainforest in the world (after the Amazonian basin), and reported as the less studied20. We used a dataset of 175 1-ha field plots established in natural stands of moist tropical forests and scattered across 8 sites from western Cameroon to eastern Democratic Republic of the Congo (Fig. 1, and see Supplementary Table S1 online), to answer the following questions: Do the largest trees mirror the AGB and diversity of the entire forest? How does Central African biomass hyperdominance compare SCIENTIFIC REPORTS | 5:13156 | DOI: 10.1038/srep13156 2 www.nature.com/scientificreports/ KorupMNgovayang abounie SE Cameroon All sites Mbaiki Malebo Yangambi Ituri Lenda 100 a 1.0 b 700 c ) 600 80 0.8 ) 500 Btot (% GB tot) A AG 60 0.6 400 ion of rt 300 40 0.4 B tot (Mg/ha AG 200 20 R² (prediction of 0.2 100 Mean propo 0 20 largest trees 0 100 largest trees 0.0 0 100 200 300 400 500 600 050 100 150 200 250 300 0 100 200 300 400 500 600 700 Cumulated number of largest trees Cumulated number of largest trees AGB of the 20 largest trees (Mg/ha) 100 d 1.0 e f 150 ) 80 0.8 60 0.6 100 ion of species (% rt 40 0.4 50 20 0.2 Species tot richness Mean propo R² (prediction of species tot richness) 0 20 largest trees 100 largest trees 0.0 0 0 100 200 300 400 500 600 050 100 150 200 250 300 0510 15 20 Cumulated number of largest trees Cumulated number of largest trees Species richness in the 20 largest trees Figure 2. Proportion and prediction of the entire above-ground biomass (AGBTOT) and species richness (speciesTOT) from the largest trees.